They tend to cluster in the general shape of a ball; although usually a bit flatter than a true sphere. The bigger the colony size the bigger the ball and the more frames they enclose. A small cluster may just reside between 2 frames. They tend to move up in the winter and will form a ball in the open space if there is a gap above your frames or missing comb. That’s when they can starve if it gets real cold and they’re in a ball that doesn’t enclose much honey. The density of the ball is a function of temp, the colder it is inside the tighter the ball and the more critical it is to have honey inside the ball. The warmer the hive, the less dense the ball and the bigger it expands; enclosing more honey.

Too warm can be a bad thing in Michigan and too cold definitely kills a lot of bees here. My bees seem to do best with something in between the extremes. If you have an insulated hive, the bees have more control over their winter environment and that allows them to keep the hive warmer which allows the cluster to be more mobile.

The cluster of bees make a very modest amount of heat in the winter, reportedly on the order of 20 watts. With that 20 watts of heat, the bees can warm up their hive to a degree IF the hive is insulated. So people don’t have the heat the hives, the bees will do it naturally….if they are insulated. Wood hives is akin to single pane glass, any heat the bees makes is quickly conducted away through the ¾” thick wood in a typical hive. Wood hives are bitter cold when it is bitterly cold outside. Insulated hives are just cool/cold when it is bitterly cold outside.

I have experimented with electrically heated hives and with super insulated hives. In my experience it is possible for the bees to get too warm in the winter and that causes its own set of problems. In my climate, the bees have done best if they maintain a cluster in the winter. If it gets too warm, the bees will break cluster and that has led to some problems for me.

I’ve seen the following bad things happen if a hive is too warm in the winter:

1.) More bees will attempt to fly in the snow and in sub freezing temps. Bees seem to lose their sense of orientation in the snow. If they land in the snow, it cools off their bodies and they’re goners. Yes, you naturally lose bees over winter no matter what, but I have seen many younger bees die in the snow as they crawled out of a hive that was too warm. You need those young bees in the spring if you want a strong buildup.

2.) I’ve had cases where the bees have completely broken cluster in the middle of winter and become so excited they heated the hive to 90F. The hives were buzzing and acting just like summer hives and consuming more honey than their cooler/normal neighbors. In my cases, those bees croaked unless I was able to get them cooled down and back into cluster.

3.) If the hive gets too warm, you risk the pests starting to reproduce. In my area, I only have to contend with wax moths. If a hive is warm enough, the wax moths will multiply even in the winter. The bees don’t seem to patrol the comb as diligently in the winter as they do in the summer, so you can end up with a hive full of moths come spring.

Don’t get me wrong, I am in favor of warm hives during winter; but not hot ones. The bees do great in a warm hive whereas they croak in a hot hive and croak in a bitterly cold hive in my climate in my bee yard.